Manufacture of paper of good wet strength



Sept, 11, 1945. K. J. MacKENZlE EIAL 2,334,632

MANUFACTURE OF PAPER OF GOOD WET STRENGTH Filgd Dec. 10, 1940 r-ABJORBENT PAPERSHEET C0N77UN/N6 POLYMER/C REACT/0N PRODUCT 0F POLYHYDR/C' ALCOHOL AND BOR/C 146' ID IJCE'NATETH J. MCKENZIE ROBERT S. BRYCE INV ENTORS 2-)" 5Y2 9 ATTORNEYS Patented Sept. 11, 1945 NET ,1

MANUFACTURE OF PAPER OF GOOD WET STRENGTH Kenneth J. MacKenzie and Robert S. Bryce, Rochester, N. Y., assignors to Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey Application DecemberlO, 1940, Serial No. 369,430

4 Claims.

This invention relates to the manufacture of paper having both a high wet strength and high water absorbency. Y

It is commonly recognized that ordinary waterleaf or unsized paper has a high absorbency for water or other liquids making such paper useful for blotters, toweling and the like. However, ordinarily this paper is given an extraordinary thickness in order to hold it together when wet, due to the low wet strength of ordinary unsized paper sheeting. In order to enhance the wet strength of paper, various sizing materials have been added thereto. Although this has corrected the lack of wet strength, the presence of sizing materialssuch as rosin, glue, regenerated cellulose or cellulose acetate, has decreased the water absorbency. Thus in no case, using those sizing materials, has anyone been able to obtain a paper having the absorbency of waterleaf paper and at the same time maintain the wet strength.

One of the uses to which absorptive paper is put is in making photo tissue. The paper is coated with a light sensitive layer, such as a bichromatcd gelatin. The photo tissue may then be exposed to light as desired and is pressed onto a copper plate with the coating surface touching the plate. The gelatin thereby sticks to the plate and the paper is stripped ofl. The paper most satisfactory for this purpose has a high wet strength and good absorbency of water to hasten the strip- Di g off of the paper therefrom.

One object of our invention is to provide a paper of high wet strength and high absorbency. Another object of our invention is to provide a paper which facilitates its stripping from a gelatin layer in the use of photo tissue. Other objects will appear herein.

We have found that if paper is sized with the resinous or viscous reaction product of a polyhydric alcohol and boric acid, a paper is obtained having a wet strength much superior to any unsized paper and yet having the same water absorbency characteristics. We have further found that if this reaction product of polyhydric alcohol and boric acid is added to a regular gelatin or glue sizing, the usual wet strength developed by the sizing will be obtained but the paper will have an absorbency equivalent to very slack sized 'ior use in our process, is described in U. 8. Patout No. 1,953,741 of Harry Bennett. By incorpo-- rating a very small amount of such a material, for example a glycerin borate resin, in paper, in

tained which is eminently suitable for toweiing, photo tissue or for other purposes where both high wet strength an high absorbency are desired. By means of our invention paper, having a thickness no greater than that ordinarily employed for paper, can be subjected to moisture is not objectionable.

The glycol borate resin may be incorporated into the paper either by adding it to the beater or by dipping a sheet of the paper into a vessel containing a water solution of the glycol borate and allowing the sheet to dry. Another method by which the glycol borate may be applied. is by passing the sheet, as a continuous web, through a trough containing a water solution of the glycol borate followed by drying. We have found that when a tissue, prepared in accordance with our invention, is used in the making of a photo tissue, it permits of rapid stripping of the paper from the gelatin layer in use. Whereas formerly with the best known types of photo tissue the stripping time or time for removing the paper from the gelatin layer has been 34 minutes, the photo tissue, using the paper of our invention, permits a stripping time of 9 or 10 seconds.

The accompanying drawing illustrates a photo tissue in accordance with our invention. This photo tissue is made up of support consisting of an absorbent paper. sheet having substantially uniformly distributed therein 1-10% of a stable, resinous, water-soluble polymeric reaction product of a polyhydric alcohol, such as glycerol or glycol, and boric acid. If desired, this sheet may also contain a small amount (not more than 5%) ofa water-dispersible sizing material such as" glue or gelatin. This paper support is designated A in the drawing. Applied on the paper is a layer or a photo-sensitive gelatin layer designated C. This layer may be, for instance, bichromated gelatin of the type which is sensitive to light.

For the preparation of photo tissue from a paper of best quality, it is desirable that a refined, high alpha, bleached sulflte pulp be employed in making that paper in accordance with our invention. Nevertheless, other paper making celluloses may be employed as, for instance, unbleached sulflte, bleached or unbleached kraft pulp, cotton or any other-cellulose which may be converted into paper. The paper, prepared in accordance with out invention, a product is obaccordance with our invention, not only is useful for photo tissue but may also be employed in the photographic art generally wherever a paper base, which is to be stripped from the photographic emulsion, is employed, such, for instance, as for stripping film. The paper of our invention is also useful for toweling, napkins, cleaning tissues, diapers, or the like. Due to the antiseptic properties of the paper of our invention, it may contact the most delicate skin without causing chapping or irrlrtation. For the making of these products the paper stock which is used should be either unbeaten or beaten only to such an extent that the absorbency characteristics of the resultant paper are not appreciably affected.

The glycol borate may be applied to the paper base either by immersion or spraying, or it may be spread on the face of the base by means of an applicator roll. If desired, it may be introduced in the bulk pulp, such as in the beater or sometime prior to the introduction of the pulp into the paper-making machine.

It is desirable to incorporate atleast one percent (based on the weight of the pulp) of the glycol .borate resin into the pulp which is employed. We have sound that there is no advantage in incorporating more than three percent of the borate but, if desired, amounts up to five percent or even up to ten percent may be-used if economy is a secondary consideration.

One very suitable method we have found for making paper, in accordance with our invention, is to use a slightly beaten paper-making stock of a nicely bleached high alpha cellulose suliite pulp. After the stock has been formed into a thin sheet on a papermaking machine. it is passed through a sizing ,bath containing about five percent of glue and about three percent of the glycol borate resin. The paper ordinarily will albsonb three percent of the glue and approximately 1 of theglycol borate. Upon drying, a product is obtained having an extremely high wet strength and a water absonbency which is but little less than a paper in which no sizin was used in its preparation.

Another method of preparing paper in accordance with our invention is to slightly beat papermaking stock in which the concentration of glycol borate resin in the water in the beater is approximately three percent. It is desirable here to incorporate a mordanting material in the heater to aid in fixing the resin on the cellulose fibers. Basic aluminum sulfates are particularly suitable for use in the beater with the resins :be free stock or in other words not unduly beaten or otherwise gelatinized thus assuring a web of an absorbent character. When high alpha pulp is used a beating of 1-2 hours is not usually too long while with ordinary pulp such as ordinary sulflte or kraft either bleached or un- (bleached, a beating ofv l-2 hours would probably unduly gelatinize the pulp and thereby deleteriously affect the absorbency characteristics of the web prepared therefrom.

For making of paper for photo tissue. the use of a high alpha sulfite pulp is preferred due to the particular nature of photographic processes. It is also desirable to make a thin-sheeting, such as approximately .005 in., although there is no objection to making a thicker sheeting for this purpose. A thickness greater than .005 in. is ordinarily unnecessary.

For toweling, diapers, napkins and the like, it is preferred, for reasons of economy, to use ordinary pulps, kraft or sulfite, bleacher or semi-bleached rather than high alpha pulp. The thickness of the paper for those purposes depends somewhat on the amount of liquid which it will be necessary to absorb. Paper produced in accordance with our invention is also useful employed for sizing paper in accordance with.

our invention; however, other mordants (this being a. well-known class) may be found useful in this connection depending on the conditions of operation and the properties desired in the finished product. The pulp is then run out onto a paper-maklng'machine and .forms a fairly thin sheet. When in sheet form it is passed through a sizing solution consisting of a five percent solution of glue in water, which solution also contains one percent of the glycol borate. .A product is obtained which, when used for photo tissue, will give a stripping time of approximately ten seconds. For some uses,'such as for toweling, diapers, napkins and the like. a thicker sheet is desirable so that more water may be absorbed thereby. Obviously the same-effect may be obtained by using a thin sheet doubled, but the use of a single sheet for those purposes is pre- 'ferred.

The pulp which is employed for absorbent sheeting in accordance with my invention should for'wrapping material where moisture is present such as in wrapping the roots of nursery stock. A paper having poor wet strength would disintegrate when so used whereas our paper, when used for the inner wrappings in such a situation. retains both its strength and the necessary moisture.

It is possible to have up to 5% of a sizing material such as gelatin or starch in a paper sheet in accordance with our invention without appreciably affecting the water-absorbent properties of the sheet. Therefore, our invention includes also paper in which besides the glycol borate resin, up to 5% of some other sizing material may be present.

We claim:

1. A photo tissue essentially consisting of an absorbent paper sheet, characterized by high wet strength and high water absorbency, having substantially uniformly distributed therein l-l0% of a stable, resinous, water-soluble polymeric reaction product of polyhydrlc alcohol and boric acid, and not more than 5% of a water-dispersible paper-sizing material, which paper sheet has a photo-sensitive gelatin layer thereon.

2. A photo tissue essentially consisting of an absorbent paper sheet, having substantially uniformly distributed therein a mixture of approximately 1 /z% of a glycol borate resin and approximately 3% of glue, which paper sheet has thereon a blchromated gelatin layer.

3. A photo tissue essentially consisting of an absorbent paper sheet having substantially uniformly distributed therein 1-10% of a stable, resinous water-soluble polymeric reaction product of glycerol and boric acid and not more than 5% of a water-dispersible paper-sizing material, which paper sheet has a photo-sensitive gelatin layer thereon.

4. A photo tissue essentially consisting of an absorbent paper sheet, having substantially uniformly distributed therein l-l0% of a stable,

resinous water-soluble polymeric reaction product 

